The machine looks like the offspring of an Erector Set and an inkjet printer.

The “ink” feels like applesauce and looks like icing. As nozzles expel the pearly material, layer by layer, you imagine the elaborate designs this device could make on gingerbread cookies.

But the goo is made of living cells, and the machine is “printing” a new body part.

These machines — they’re called three-dimensional printers — work very much like ordinary desktop printers. But instead of just putting down ink on paper, they stack up layers of living material to make 3-D shapes. The technology has been around for almost two decades, providing a shortcut for dentists, jewelers, machinists and even chocolatiers who want to make custom pieces without having to create molds.

In the early 2000s, scientists and doctors saw the potential to use this technology to construct living tissue, maybe even human organs. They called it 3-D bioprinting, and it is a red-hot branch of the burgeoning field of tissue engineering.

In laboratories all over the world, experts in chemistry, biology, medicine and engineering are working on many paths toward an audacious goal: to print a functioning human liver, kidney or heart using a patient’s own cells.

That’s right — new organs, to go. If they succeed, donor waiting lists could become a thing of the past.

Tony Atala, director of the Wake Forest Institute for Regenerative Medicine in North Carolina, envisions what he calls “the Dell computer model,” where a surgeon could order up “this hard drive, with this much memory …,” only he or she would be talking about specs for living tissue rather than electronics.

Bioprinting technology is years and possibly decades from producing such complex organs, but scientists have already printed skin and vertebral disks (the soft tissue that grows in the spine between the vertebrae) and put them into living bodies. So far, none of those bodies have been human, but a few types of printed replacement parts could be ready for human trials in two to five years.

“The possibilities for this kind of technology are limitless,” said Lawrence Bonassar, whose lab at Cornell University has printed vertebral tissue that tested well in mice. “Everyone has a mother or brother or uncle, aunt, grandmother who needs a meniscus or a kidney or whatever, and they want it tomorrow. ... The promise is exciting.” But he warns that nothing is likely to be ready in time to help people who already need an organ. “The goal is not to squash that excitement, but to temper it with the reality of what the process is.”

The reality for now is that making such things as vertebral disks and knee cartilage, which largely just cushion bones, is far easier than constructing a complicated organ that filters waste, pumps blood or otherwise keeps a body alive.

Scientists say the biggest technical challenge is not making the organ itself, but replicating its intricate internal network of blood vessels, which nourishes it and provides it with oxygen.

Many tissue engineers believe the best bet for now may be printing only an organ’s largest connector vessels and giving those vessels’ cells time, space and the ideal environment in which to build the rest themselves; after that, the organ could be implanted.

The cells, after all, have been functioning within the body already in some capacity, either as part of the tissue that is being replaced or as stem cells in fat or bone marrow. (Donor stem cells could be used, but ideally cells would come directly from the patient.)

“The cells are actually the tissue engineers, so the people that do the work are just cheerleaders,” said Rocky Tuan, director of the Center for Cellular and Molecular Engineering at the University of Pittsburgh. “When we do tissue engineering, we are accelerating what the cells normally do. I tell people it’s assisted living, because we help the cells. We build all the houses and everything, and then we say, ‘Cells, come in and do your thing.’ ” If the cells do their thing correctly, the organ lives and grows just as the original once did.

Another huge challenge is common to much new research: lack of money.

“If the federal government created a ‘human organ project’ and wanted to make the kidney, I literally think it could happen in 10 years,” said chemical engineer Keith Murphy, co-founder of Organovo, a firm that makes and works with high-end bioprinters. But that would require a massive commitment of people, resources and billions of dollars, he said.

Once scientists get over the financial and technical hurdles of bioprinting, they will have to square the process with the Food and Drug Administration, which will have to decide how to regulate something that is not simply a device, a biological product or a drug, but potentially all three.

Before printed organs are implanted into people, bioprinting may be used in other ways. Murphy’s group is working on a project that will replicate tissue for testing the effects of medications, particularly cancer drugs. This could eliminate some of the drawn-out, trial-and-error process of trying a series of drugs on a person before finding one that works.

While a complex organ would be the holy grail for most tissue engineers, some like to look even farther ahead, straight into science fiction.

“If one can bioprint functional human organ constructs, then bioprinting a whole human — or whatever will be the name for such a creature — is just a logical extension,” said Vladimir Mironov, a pioneer in the field who is working with computer companies to design better bioprinting software.

Others don’t know why anyone would want to do that.

“It’s a visionary idea,” said Mironov’s colleague Jonathan Butcher of Cornell, whose lab is working on printing heart valves. “But the usual method of human reproduction works pretty well.”